1. Field of the Invention
The present invention is related to a magnetic resonance diagnostic apparatus which has a radio frequency coil arranged in a gantry, and a radio frequency coil unit used for this magnetic resonance diagnostic apparatus.
2. Description of the Related Art
In a magnetic resonance diagnostic apparatus, generally, a radio frequency coil (referred to hereinafter as an RF coil) such as a whole body coil (referred to hereinafter as a WB coil) is arranged inside a gantry.
The RF coil generates heat by energization. Conventionally, the RF coil was cooled by natural convection of the surrounding. Therefore, generally, no special cooling treatment was applied.
Therefore, there was a problem that heat generated by the RF coil increased the temperature of the imaging space inside the gantry and made the subject placed in this imaging space uncomfortable.
In order to deal with this, a cover has been discussed on being arranged leaving a certain space from the RF coil, to prevent heat generated by the RF coil from being transferred to the imaging space. However, in this case, there was a problem that the cover made the imaging space small and may give the subject an oppressive feeling.
Further, a structure to cool the RF coil by using cooling water is suggested in, for example, Jpn. Pat. Appln. KOKAI Publication No. 11-244255. However, according to the structure known by the reference, the structure of the cooling unit would become elaborate, and the accommodating space thereof would become large. Therefore, there has been a problem that the reduced imaging space may give the subject an oppressive feeling.
Under such circumstances, the applicant of the present invention suggests in Jpn. Pat. Appln. KOKAI Publication No. 2009-142647 a structure in which a space is formed between a member holding the RF coil (hereinafter referred to as a base portion) and a cover to generate a flow of cooling air in this space, in order to air-cool the RF coil.
However, sometimes the RF coil is removed from the gantry for maintenance. Therefore, the RF coil is desired to be taken out easily from the gantry. Accordingly, in the invention, an RF coil unit which is independent from the gantry is formed by the RF coil and the base portion holding the RF coil. The RF coil unit is not fixed to the gantry but is used in a state of being fitted in the imaging space. Further, when attaching or detaching the RF coil unit to or from the gantry, the RF coil unit is taken in and out from the imaging space from the opening of the imaging space of the gantry. Therefore, the outer diameter of the RF coil unit should be smaller than the inner diameter of the imaging space. Attachment/detachment of the RF coil unit would become easier as the difference between the outer diameter of the RF coil unit and the inner diameter of the imaging space increases. However, at the same time, as the difference between the outer diameter of the RF coil unit and the inner diameter of the imaging space increases, the base portion becomes less close to the wall surface forming the imaging space. Therefore, the structure suggested by Jpn. Pat. Appln. KOKAI Publication No. 2009-142647 is defective in that, since the cooling air would flow out of the imaging space, cooling efficiency of the RF coil would deteriorate.
It is considered that by mounting a seal member having resiliency on a position where the base portion is adjacent to the cover, air-tightness formed between the RF coil unit and the cover can be secured to a certain extent while enabling attachment/detachment of the RF coil unit with respect to the gantry. However, it would still be difficult to attach or detach the RF coil unit to or from the gantry as the above mentioned tightness improves.